1. Field of the Invention
The present invention relates to a length measuring apparatus employing an ultrasonic magnetostrictive delay line in use, for example, in measuring a level surface of gasoline in a gasoline tank, detecting the stroke of a piston rod when assembled into a hydraulic cylinder or detecting positions of movable parts of a variety of industrial machines and so on.
2. Description of the Related Art
Length ultrasonic linear measuring apparatus that have hitherto been proposed use an ultrasonic magnetostrictive delay line whose length is extended or reduced with the application of a magnetic field. In the conventional measuring apparatus, a non-reflection supporting member made of a shock-absorbing material, such as a rubber or the like, is attached to one end portion of the ultrasonic magnetostrictive delay line in order to damp an undesired reflected wave generated by ultrasonic vibration.
In the above conventional measuring apparatus it is difficult to damp the undesired reflected wave completely. Thus, reflected ultrasonic waves cross each other so as to interfere with the detection pulse whereby the detection pulse is disturbed. This results in the disadvantage that position cannot be detected with high accuracy.
Further, if strong ultrasonic vibration were generated in order to obtain a stable and large detection pulse, it would become impossible to damp reflected waves and to gradually dissipate the reflected waves.
Furthermore, even when the undesired reflected wave is completely removed by using the non-reflection supporting member as described above, it is unavoidable that the whole of the apparatus becomes large in size due to the provision of the non-reflecting supporting member.